//编写你自己的StrBlob类，包含const版本的front和back。
#include<iostream>
#include<vector>
#include<string>
#include<initializer_list>
#include<memory>
#include<stdexcept>
using namespace std;
class StrBlob
{
public:
	typedef vector<string>::size_type size_type;
	StrBlob();
	StrBlob(initializer_list<string> il);
    // 	StrBlob& operator=(StrBlob& t) {
	// 	data = make_shared<vector<string>>(t.data->begin(), t.data->end());
	// 	return *this;
	// }
	// StrBlob(StrBlob& Str) {
	// 	data = make_shared<vector<string>>(Str.data->begin(), Str.data->end());
	// }
	size_type size() const { return data->size(); }
	bool empty() const { return data->empty(); }
	void push_back(const string &t) { data->push_back(t);}
	void pop_back();
	string& front();
	const string& front() const;
	string& back();
	const string& back() const;
private:
	shared_ptr<std::vector<std::string>> data;
	void check(size_type i, const std::string &msg) const;
};
StrBlob::StrBlob() :data(make_shared<vector<string>>()) {}
StrBlob::StrBlob(initializer_list<string>il) :
	data(make_shared<vector<string>>(il)) {}
void StrBlob::check(size_type i, const string &msg)const
{
	if (i >= data->size())
		throw out_of_range(msg);
}
string& StrBlob::front()
{
	check(0, "front on empty StrBlob");
	return data->front();
}
const string& StrBlob::front() const
{
	check(0, "front on empty StrBlob");
	return data->front();
}
string& StrBlob::back()
{
	check(0, "back on empty StrBlob");
	return data->back();
}
const string& StrBlob::back() const
{
	check(0, "back on empty StrBlob");
	return data->back();
}
void StrBlob::pop_back()
{
	check(0, "pop_back on empty StrBlob");
	data->pop_back();
}

int main()
{
	StrBlob b1;
	{
		StrBlob b2 = { "a","an","the" };
		b1 = b2;
		b2.push_back("about");
		cout << b2.size() << endl;
	}
	cout << b1.size() << endl;
	cout << b1.front() << " " << b1.back() << endl;
	const StrBlob b3 = b1;
	cout << b3.front() << " " << b3.back() << endl;
	return 0;
}